The Colour of Heaven

From the author's site (see link): The novel is set mainly in Italy, from 1295 until 1315. An abandoned child is taken in by Theresa, the wife of a glass-maker on the island of Murano in the Venetian lagoon. The baby, Paolo, grows up short sighted but has a distinct way of looking at the world. He befriends a painter and sets out on The Silk Route with two friends - Jacopo, a Jew, and Salek, a Muslim - all children of Abraham, in search of the perfect colour blue, the colour of heaven. They travel in search of understanding, sight, love and meaning.